This invention relates to diaphragm gas meters and, more particularly, to a temperature compensating tangent assembly for use therewith.
Positive displacement diaphragm gas meters typically are provided with a tangent assembly which drivingly couples the diaphragm driven flag assembly to a crank which is in turn coupled to open and close the slide valves of the meter. One complete cycle of the meter causes a single rotation of the tangent assembly. The stroke of each diaphragm is determined by the distance from the center of rotation of the tangent assembly to the wrist of the tangent assembly. This is known as the "tangent throw". The tangent throw therefore determines the gas volume passed through the meter for each diaphragm stroke.
As the temperature of the gas increases, its volume increases for the same energy content. It is therefore desirable to increase the volume of gas passing through the meter for one complete cycle of the meter as the temperature of the gas increases. It is known to provide temperature compensating tangent assemblies which increase the tangent throw as the gas gets warmer, thereby requiring a greater volume of gas for each cycle of the meter.
In the past, various arrangements have been proposed to provide a temperature compensating tangent assembly which varies the tangent throw in accordance with variations in the temperature of the gas. It was previously believed that it was desirable to maintain as linear as possible the radial path of movement along which the wrist is adjusted toward and away from the axis about which it rotates. However, the Applicant herein has discovered that this linearity of movement adversely affects the timing of the meter valves. It is therefore an object of the present invention to provide a temperature compensating tangent assembly for a diaphragm gas meter which keeps the meter timed correctly over a wide range of temperatures.